The present invention relates generally to position sensing, and, in one embodiment, to a non-contact absolute position sensor for sensing the position of an automobile seat along a seat track.
In a wide variety of applications it is advantageous or necessary to sense the position of a linearly or rotationally movable element. For example, in automobile seat applications the seat may be linearly movable, either manually or automatically via electro-mechanical means, on an associated track assembly. A sensor may provide a signal representative of the linear position of the seat on the track for a variety of purposes, e.g. to control deployment of an air bag, to control the electro-mechanical actuator that causes translation of the seat in connection with a seat position memory feature, etc.
For a seat position application, it is increasingly desirable for a sensor to provide multiple position outputs for purposes of ascertaining occupant position. For example, in applications where seat position is used to control air bag deployment early configurations involved only single stage air bag systems. A single stage air bag deploys with a known deployment force that may not be varied. In this application, seat position information was used only to determine when the airbag should be deployed.
However, the advent of dual stage air bags, i.e. air bags that may be deployed with two distinct deployment forces, has necessitated increased resolution in position sensing. Also, the industry is now moving to variable stage airbags where the deployment force may be varied depending upon occupant position and classification. Variable stage airbag configurations will require a sensor that can detect multiple seat positions for use in determining the appropriate deployment force.
Known automobile seat position sensors, however, provide outputs associated with only a limited number, e.g. two, seat positions. In addition, many conventional seat position sensor configurations utilize contacting technology, e.g. resistive or wiper contact configurations, and are thus mechanically coupled to the seat track mechanism. This mechanical coupling tends to generate undesirable noise and system wear.
Also, when such sensors are assembled to a seat track, sensor calibration is not reliable. Where the sensor is used for airbag deployment, proper system operation and, indeed, the safety of vehicle passengers, depends on accurate sensor calibration. Moreover, existing configurations present difficulties when a sensor malfunction occurs. To replace such a sensor, the entire track assembly must be discarded to avoid the possibility that the dealer would improperly assemble or calibrate the sensor.
There is thus a need for a reliable sensor for providing an output associated with multiple positions of a vehicle seat along a seat track. There is a further need in the art for a seat track position sensor that may be properly calibrated in a simple manner and efficient manner.
According to one aspect of the invention, there is provided a position sensor including: a reduction gear train having an input gear and an output gear. The input gear is configured for coupling to an output shaft of a drive motor for driving a vehicle seat on an associated seat track, and a magnet disposed on the output gear for rotation therewith. A Hall Effect sensor is disposed adjacent the magnet for providing a sensor output signal in response to rotation of the magnet. The Hall sensor may be a linear Hall sensor for providing a linear output proportional to the number of revolutions of the drive shaft and, hence, the position of the seat on the seat track.
According to another aspect of the invention there is provided a lock out mechanism for a position sensor. The mechanism includes a housing defining an opening for receiving an output shaft of a drive motor for driving a vehicle seat on an associated seat track and a lock out arm biased toward the opening. The lockout arm is configured to move over the opening upon removal of the output shaft from the opening, thereby preventing reinsertion of the output shaft into the opening.
According to further aspects of the invention there is also provided a method of sensing the position of a vehicle seat and a method of calibrating a vehicle seat position sensor.